87 lebaron 2.5 rod bearings

I just got a 87 Lebaron with a 2.5L (vin K) engine that has a rod noise amongst other things. I thought it best to fix the engine first b4 putting money into the AC and cooling system etc.
So, I jacked it up and removed the pan and carrier assembly and got the rod bearings off. All the bearings are worn/scoured and are stamped standard size. I was wondering if I should just replace the rod bearings with a standard set or should I check the main bearings as well?
The engine only has 80K miles on it, I cant understand why the rod bearings are bad in the first place - maybe the owner ran it low on oil or something. The journals seem ok, was wondering if I should measure the diameter on each to verify if they are true or just go ahead and slap on a new set of bearings and not worry about the mains or the oil pump etc.
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